The Severe Asthma Research Program III is an NIH cooperative agreement involving 7 clinical centers that encompass a multidisciplinary partnerships between asthma clinician-scientists and scientists with expertise in immunology, pulmonary physiology, molecular genetics, molecular phenotyping, imaging, and bioinformatics. These clinical centers will jointly recruit volunteers with asthma for an observational longitudinal follow-up study. However, centers will also conduct specific mechanistic research projects at each participating institution. The University of Pittsburgh's SARP III study will determine the molecular and clinical stability of asthma phenotypes over time.